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The efficiency of transformation of point mutations depends upon base pair mismatches during the recombination process. For low-efficiency markers, the genetic information carried on the donor deoxyribonucleic acid is preferentially lost. To understand this elimination process, we investigated the effect of the size of donor deoxyribonucleic acid on the relative efficiency of low-efficiency point mutations. The deoxyribonucleic acid was shortened either by mechanical shearing or by restriction enzyme treatments. The results indicate that transformation by low-efficiency markers was not affected by shortening the distance between them and the end of the molecule any more than was transformation by the other markers. Moreover, no lethal event could be detected for either cell or chromosomal marker survival. These data do not exclude the double-strand-break hypothesis that was proposed to explain the loss of genetic information for low-efficiency markers, but they offer no support for it.
Lefèvre et al. (Sun,) studied this question.